Improving the Technology Readiness Level of the 6000-m capable Conductivity Temperature Depth sensor mounted on Deep Argo floats

Lead PI:  Nathalie Zilberman, University of California San Diego
Start Year: 2018 | Duration: 3 years
Partners: Scripps Institution of Oceanography, Seabird Scientific, NOAA Pacific Marine Environmental Laboratory

The extension of Core Argo (0-2000 m) into the deep ocean below 2000 m, is needed for many objectives, including closing the regional and global budgets of heat, freshwater, and steric sea level on annual to decadal time-scales, and for accurate estimation of velocity and transport in the deep-ocean circulation. The Deep Argo Program will provide the required global coverage of full-depth temperature and salinity at 5° latitude x 5° longitude spacing, every 15 days.

The development of the new SBE-61 CTD mounted on Deep Argo floats, is critical for the implementation of the Deep Argo array. The SBE-61 is approaching, but has not achieved the target accuracies of 0.001°C, 0.002 PSS-78, and 3 dbar for temperature, salinity, and pressure, set by the Deep Argo community. The aim of this proposal is to validate the accuracy and stability of salinity and pressure, and to advance the SBE-61 CTD to Technology Readiness Level 9.

Laboratory comparisons will be used to identify a potential sensor candidate for replacement of the Kistler pressure sensor, currently mounted on the SBE-61 CTD. A 14-day research cruise is planned in the Southwest Pacific Deep Argo pilot array, to improve estimates of the pressure correction of the conductivity cell, and for comparative testing of the SBE-61 CTD equipped with the new pressure sensor, with the SBE-911 shipboard CTD. Salinity observations from conventional (0-2000 m) SOLO floats and Deep SOLO floats, will be used to improve correction for the conductivity cell thermal mass error in SBE-61 CTDs. Deep SOLO floats equipped with the Kistler sensor on the SBE-61 CTD, and the pressure sensor candidate mounted separately, will be deployed during the research cruise, to assess the time dependency of the pressure and conductivity errors.